Age-related changes and inheritance of lactate transport activity in red blood cells

In red blood cell membranes, the activity of the main lactate carrier, H+-monocarboxylate co-transporter (MCT), varies interindividually and its distribution is bimodal. To show the repeatability of MCT activity, 2 to 5 blood samples were taken, at an interval of approximately 1 year, from 51 Standardbred horses, age 2 weeks-8 years, for a total of 128 observations. The horses could be divided into low (LT) and high (HT) lactate transport activity groups. Age significantly affected (P<0.05) MCT activity such that activity was highest in foals, reached a nadir at 2-3 years, and tended to increase again thereafter. Interindividual variation was not sufficiently high to allow a horse to switch from the LT-group to the HT-group, or vice versa. When MCT activity from 4 sires, 15 dams and their 52 offspring was analysed, the data showed that MCT activity is heritable and supported the hypothesis that low MCT activity was caused by a recessive allele in a single autosomal locus. Because MCT activity affects RBC lactate concentrations, the phenomenon may be physiologically significant.